The present invention relates to a method of operating a hybrid vehicle and, in particular, to a method of operating a hybrid vehicle which has an internal-combustion engine and an electric drive provided for generating vehicle propulsion.
In the following, the term “hybrid vehicle” will apply to a vehicle having an internal-combustion engine and at least one electric motor provided for generating vehicle propulsion. A hybrid vehicle of this type can selectively be operated exclusively by the electric motor (purely electric operating mode) in a first operating mode or, in a second operating mode in which the internal-combustion engine as well as the electric motor will drive the vehicle. Naturally, the vehicle can also be operated in a third operating mode exclusively by the internal-combustion engine.
When the vehicle is operated in the first operating mode, i.e. purely electrically, the driver has to actuate the accelerator in a very sensitive manner. When the desired drive torque prompted by the driver by way of the accelerator pedal exceeds the torque maximally producible by the electric motor, a change takes place to the second operating mode by connecting the internal-combustion engine, which the driver would like to avoid, for example, when driving in the city. The situation in which the electronic system changes to the second operating mode by connecting the internal-combustion engine occurs particularly when the driver wants to maximally use the power offered by the electric motor, i.e. when driving at the upper electric power limit.
It is an object of the invention to indicate a method of operating a hybrid vehicle, wherein the internal-combustion engine is additionally started less frequently than in the case of conventional hybrid driving.
This and other objects are achieved by a method of operating a hybrid vehicle which has an internal-combustion engine and an electric drive provided for generating vehicle propulsion. The vehicle is selectively driven in a first operating mode, exclusively by the electric drive, in a second operating mode by the internal-combustion engine and by the electric drive, or in a third operating mode, exclusively by the internal-combustion engine. In the first operating mode, the driver predefines a desired drive torque by way of a selection element. The first operating mode is maintained at least in some operating conditions even if the desired drive torque is greater than a maximal drive torque that can presently be provided by the electric drive. Advantageous embodiments and further developments of the invention are described and claimed herein.
The invention is based on not additionally starting the internal-combustion engine in all situations in which the desired drive torque prompted by the driver by way of the selection element (for example, the gas pedal) exceeds the maximal drive torque that can presently be provided by the electric motor.
Rather, the invention consists of continuing to drive in the first operating mode, i.e. purely electrically, in at least some or in defined operating conditions, even if the desired drive torque is (slightly) greater than the maximal drive torque that can presently be provided by the electric motor. When sensitively actuating the selection element—which, in the following, is called an accelerator pedal—the driver therefore feels that, starting at a defined desired drive torque, i.e. starting at a defined position of the accelerator pedal, the overall drive torque will at first not increase even if the actuating of the accelerator pedal is slightly more intense. As a result, the driver receives an “acknowledgment” that the “electric drive” has reached its actual power and torque limit.
In contrast to conventional hybrid vehicles, a “slight” exceeding of the desired drive torque corresponding to the “power limit” or “torque limit” of the electric drive therefore does not immediately result in a change to the second operating mode, i.e. not directly in the starting of the internal-combustion engine.
Rather, the first operating mode is maintained as long as the desired drive torque prompted by the driver by way of the accelerator pedal is greater by, at the most, a predefined differential drive torque than the maximal drive torque that can presently be provided by the electric motor. When, while actuating the accelerator pedal, the driver reaches the position which corresponds to the maximal drive torque that can presently be provided by the electric motor, the driver can continue to depress the accelerator pedal by a pedal travel that corresponds to the differential drive torque, without an additional starting of the internal-combustion engine.
According to a further development of the invention, the amount of the differential drive torque is a function of how fast the driver actuates the accelerator pedal. More precisely, the amount of the differential drive torque is a function of how fast the driver actuates the selection element when exceeding the accelerator pedal position to which the maximal drive torque corresponds that can presently be provided by the electric motor. When the accelerator pedal position is described by an angle coordinate or by a travel coordinate, the differential drive torque is a function of the time derivation of the angle coordinate or time coordinate, i.e. of the gradient of the angle coordinate or time coordinate describing the accelerator pedal position.
According to a further development of the invention, it is provided that a change takes place to the second operating mode or to the third operating mode (pure internal-combustion engine operation) when the desired drive torque prompted by the driver by way of the accelerator pedal is greater than the sum of the maximal drive torque that can presently be provided by the electric motor and of the differential drive torque. Therefore, when the driver continues to relatively strongly depress the accelerator pedal as the maximal drive torque is reached that can presently be provided by the electric motor, the internal-combustion engine will be started and a pure internal-combustion engine operation or a combined internal-combustion engine and electric motor operation will take place.
In the case of a change from the first to the second or third operating mode, the overall drive torque at which the hybrid vehicle is driven has to be raised to the desired drive torque prompted by the driver by way of the accelerator pedal. The “raising” may take place according to a predefined function. For example, it may be provided that the overall drive torque—to the extent that it can be displayed with respect to the power—is raised according to a linear function from the maximal drive torque that can presently be provided by the electric motor to the desired drive torque.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.